Local yellowing of PVB/polyvinyl-butyral-resin material at the edges of laminated glass is a rare but serious quality defect, characterized by two approximately 5 cm yellowed areas at the edges. With an occurrence rate of nearly 100%, it has led to customer complaints and financial losses. This study identifies the root cause through production process audits, experimental validation, and microscopic testing, proposing an effective solution.
Cause Analysis
The production process of laminated glass includes cutting, edging, lamination, autoclave treatment, packaging, storage, and transportation. On-site investigations revealed that yellowing only occurs at the contact points (about 5 cm wide) with the product rack base. No yellowing was observed immediately after autoclave treatment, but it appeared after packaging and storage. In high-temperature summer conditions, defects formed more quickly (6–24 hours), and both the plastic film and rubber base at the contact points also turned yellow. Initial hypotheses included:
Local PVB /pvb-sd-1Aging Due to High Temperature: Tests placing glass on a newly maintained rack (trimmed rubber base and deepened grooves) showed no yellowing after 24 hours, ruling out this possibility.
Plastic Film Aging Contaminating PVB: Replacing the film with adhesive tape still resulted in yellowing, indicating the film was not the direct cause.
Migration of Yellowing from Rubber Material: Placing glass on a newly maintained rack prevented yellowing, confirming that aged rubber was the key factor.
Testing and Mechanism Study
Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) were used to analyze yellowed PVB and rubber materials. The findings included:
FTIR detected no significant differences in PVB or rubber composition.
GC-MS identified additional organic functional groups (e.g., benzothiazole, acenaphthylene, fluorene, anthracene) in yellowed PVB, which are rubber additives (e.g., vulcanization accelerators, antioxidant 4010NA). These substances migrated to PVB due to the "blooming" phenomenon of EPDM rubber, causing localized yellowing. High temperatures and pressure accelerated the migration, explaining seasonal variations in defect formation time.
Optimization Solutions
Three solutions were proposed based on the analysis:
Isolate Blooming Migration: Add an inorganic barrier between the glass and rubber.
Regular Maintenance of Rubber Base: Trim aged surfaces periodically.
Replace Rubber Material: Use peroxide-cured rubber to minimize blooming.
The factory adopted solution (1), reducing the yellowing defect rate to 0% while balancing cost and effectiveness.
Conclusion
The root cause of local PVB yellowing was the migration of additives from the EPDM rubber base. The isolation measure effectively resolved the issue. This method can also be applied to control yellowing defects in other interlayer materials (e.g., EVA), providing a reference for similar process challenges.
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